Nokia is to buy Trolltech, the company whose Linux-based Qt application-development framework is at the core of many PC and mobile applications.

On Monday the companies announced that Nokia was offering 16 Norwegian Kroner per Trolltech share in cash, making the total value of the deal around NOK844m (£78m). The deal has been unanimously approved by Trolltech's board of directors, and holders representing around two-thirds of Trolltech's shares and votes have also accepted the offer in advance.

Qt forms the basis of many well-known desktop applications, such as Google Earth, Opera and Skype. Qt is used to develop graphical user interfaces (GUIs) and is the main GUI toolkit for the KDE Linux project, one of the two main desktop environments for the open-source operating system — the other being Gnome. Qt's derivative, Qtopia — also a Trolltech product — is already used in millions of consumer-level mobile phones, notably in Asia and through the manufacturer Motorola.

Dr Kai Öistämö, the head of Nokia's devices unit, said in a press conference on Monday that the Finnish manufacturer would allow Trolltech to "continue in its current organisation form with full operational alignment" after the deal closes — a development expected to occur in the second quarter of this year. Nokia already uses Qt in its Nokia PC Suite application to allow mobile handsets to integrate with Windows PCs.

"Trolltech brings software talent and technologies that are proven, world-class and with wide industry support, and will ensure exciting innovations and bring new momentum to us," said Öistämö.

Öistämö said the acquisition would aid Nokia in its strategies of being "a leader of the converged world in internet mobility" and "growing consumer services and businesses solutions".

Nokia's intention is to use Trolltech's technology to develop its next generation of software horizontally across "all the major software platforms in the world", said Öistämö, who specified Series 60, Series 40, Windows Mobile, Apple OS X and Linux. However, he stressed that Nokia's existing Linux-based devices, such as the N810 tablet, would continue to use the Gnome environment rather than KDE.

"The Qt tools… allow developers to build applications across different types of devices and PCs," said Öistämö. "In practice, Qt is the only set of libraries and tools available on all desktops and on mobiles. With Qt, the services and applications can be built only once and then simply compiled using Qt tools to bring the innovation to all different software platforms, [thus allowing] a faster time to market."

"Qt also is the most compact solution within the market allowing use in [low-end] devices, where memory is quite pricey and always a constraint," said Öistämö. "Qt is a great fit with Nokia's assets and evolution plans."

Öistämö promised that Nokia would "actively contribute to the open-source community, especially KDE", and would "continue to invest in Qt, adding more advanced graphical capabilities". He also provided reassurance that, as one of Nokia's key drivers for the acquisition had been Trolltech's "talent", the manufacturer had "no plans to reduce [Trolltech's] workforce".

Speaking to ZDNet.co.uk on Monday, Trolltech's "chief troll" and co-founder, Eirik Chambe-Eng, said the companies had been in talks about the acquisition since September 2007. He also confirmed that Nokia was not currently intending to make Linux-based mobile phones. However, he suggested the manufacturer would now "evaluate" the Linux Mobile (LiMo) Foundation — of which Trolltech is a member — and other such initiatives to see if there might be a role for the company there in the future.

Chambe-Eng said that Nokia's decision to stick with Gnome for its Linux devices "makes a lot of sense". "They have an internal group that has been doing that for a long time," he said. "But they are using the Qt/X11 windowing system. It is possible to use Qt together with Gnome — KDE applications fit well into that scenario. Very few people are aware that KDE and Gnome are very compatible."

Chambe-Eng added that Nokia's decision to maintain Trolltech's existing dual-licensing model and continue feeding into the open-source community had been "very key" to Trolltech's agreement to the acquisition. According to Chambe-Eng, Trolltech has a "very special status in both the Linux and Unix community at large [and now benefits from being] part of an organisation with much more muscle than [Trolltech] had so far".

Trolltech and Nokia hope that regulatory approval will be granted by the Norwegian authorities in the next few weeks. Meanwhile, there are no firm details yet as to when Qt-based applications might appear on Nokia's Series 40 and Series 60 handsets.